Dialysis treatment of individuals suffering from renal failure requires that blood be withdrawn and cycled through a dialysis machine that performs the function of the failed kidneys. This process, termed hemodialysis, must be repeated at a regular interval (e.g., three times per week) and thus requires repeated punctures using dialysis needles. Relatively large gauge needles are required to promote the high flow rates required during dialysis. Frequent puncturing of autogenous arteriovenous access as well as prosthetic arteriovenous access with large bore needles can cause trauma, conduit degeneration, hematoma formation, pseudoaneurysm formation, loss of patency, or even hemorrhage and exsanguination.
A common technique to provide vascular access for hemodialysis, therefore, is to connect a prosthetic graft or shunt between an artery and a vein in, for example, the upper or lower extremity. Occasionally, patient complexity may also warrant access placement on the chest or abdominal wall. Conventional arteriovenous grafts (AVGs) are often constructed of a polymeric material such as expanded polytetrafluoroethylene (ePTFE) or polyetherurethaneurea.
A significant mode of failure of AVGs is related to a traumatic cannulation with the dialysis needle. This may occur as the needle traverses the anterior wall of the AVG and then continues through the posterior wall (or a sidewall) of the graft. This type of trauma causes a defect in the posterior and/or side wall of the graft and often results in hematoma formation which can ultimately lead to graft thrombosis (i.e., the formation of a blood clot inside the graft, obstructing the flow of blood therethrough) by external compression of the graft and ultimate graft failure.
Moreover, repeated punctures of the graft material (such as ePTFE) promotes coring and degeneration of the graft material which often leads to rupture of the graft, pseudoaneurysm formation, and graft thrombosis. Also, ePTFE grafts are generally not self-sealing when punctured and usually require implantation three, four or more weeks prior to puncture to allow for graft incorporation (a layer of fibrotic tissue that attaches to the outside surface of the graft). The layer of fibrotic tissue may prevent leakage of blood through the wall of the graft upon withdrawal of the dialysis needles and if cannulated before this time could lead to hematoma formation between the graft and surrounding tissue. This hematoma could cause adverse events such as graft occlusion, lack of incorporation of the graft and increased chance for infection. However, there is often very little subcutaneous tissue between the surface of the skin and the anterior face of the graft, and the above-mentioned problems may occur even after waiting for tissue incorporation.
U.S. Pat. No. 6,146,414 to Gelman, the disclosure of which is incorporated herein in its entirety, describes tube grafts having expanded regions and shields at posterior portions of the expanded regions. The shields have added rigidity relative to the tube to thereby signal to the operator when the needle tip hits a shield during cannulation. The shields are either incorporated into the tube graft or are added as a separate component during assembly, thereby adding complexity to the manufacturing process. The Gelman patent describes that the shields may be rigid or semi-rigid but only describes straight grafts (i.e., grafts without curvature). Substantially rigid shields would require that the grafts described in the Gelman patent be kept in a generally straight configuration, and such a configuration may be difficult or impossible to use at many AVG implantation sites, such as forearms and upper arms. Semi-rigid shields may allow for some bending of the graft to accommodate placement in these areas, but would reduce or eliminate the capability of the shield to prevent needle penetration through the shield or warn the operator of impending penetration. Also, bending of grafts employing semi-rigid shields could weaken the graft and/or disrupt flow characteristics for blood flowing therethrough. Finally, the Gelman patent does not recognize the need for a self-sealing graft or a portion thereof.
Self-sealing vascular access grafts have been described in, for example, U.S. Pat. No. 5,192,310 to Herweck et al., U.S. Pat. No. 7,452,374 to Hain et al., and U.S. Pat. No. 7,780,622 to Fitzpatrick et al., the disclosures of which are incorporated herein in their entireties. However, none of these patents consider the problem of dialysis needles puncturing side walls or anterior walls during cannulation. U.S. Pat. No. 6,261,257 to Uflacker et al., the disclosure of which is incorporated herein in its entirety, describes grafts with straight port chambers including self-sealing septums. The problem of puncturing side walls or anterior walls during cannulation is also not contemplated in the Uflacker patent. Even if the straight chambers were constructed of a rigid material to ostensibly provide puncture resistance, such a configuration would not be suitable for implantation in the upper or lower extremities, as described above.
Thus, there is a need for arteriovenous grafts configured to be implanted in a subject (e.g., in an upper or lower extremity of a subject) with puncture resistant posterior walls and side walls. There is also a need for such arteriovenous grafts to include self-sealing ports at the anterior surfaces of the graft. Such designs may help prevent traumatic cannulations and/or graft degeneration so as to lead to higher patency rates for arteriovenous grafts, decrease the risk of hemorrhage or infection for hemodialysis patients, and reduce overall vascular access related healthcare costs.